1. Field of the Invention
The present invention relates to a winding arrangement of an alternator for a vehicle which is mounted in a passenger car, a truck or the like.
2. Description of the Related Art
Various improvements have been proposed to make an alternator for a vehicle more compact and more powerful.
JP-A-6-46550 proposes using permanent magnets for increasing the output power of an alternator. However, in order to comply with the demand for reducing the size of the alternator, the size of the cooling fan must be reduced. This reduces an amount of the cooling air, while Joule heat and, in turn, temperature rise increases as the output power increases. In other words, in order to provide a compact and powerful alternator, it is important to control the temperature rise, in particular, the heat dissipation of the armature coil in a limited space.
In view of these circumferences, JP-A-7-194060 discloses a water cooling system for an alternator instead of the air cooling system to increase the cooling effect on the alternator. However, it is apparent that the water cooling system inevitably requires water pipes and a water jacket disposed in the alternator and, therefore, the size and weight thereof increase.
In a common air cooling system of the alternator, the coil-ends of an armature coil are mainly cooled, and various improvements thereof are proposed in the following publications: JP-B2-4-24939, JP-A-63-59744, JP-Y2-1-27406 and JP-A-57-132743.
Each of those system has the following problems although it has some cooling effect on the alternator.
In JP-B2-4-24939, a number of spaces are provided between respective phase-windings so that cooling air can pass therethrough. However, the cooling air blows only on a part of the winding as the parallel flow whose cooling effect is proportional to 0.6 th power of a wind velocity and is not sufficient as compared with the right-angled flow whose cooling effect is proportional to a square of the wind velocity. FIG. 3 of the publication shows a coil end having wires spaced apart from one another. Cooling air passes the spaces between the wires. Although such a structure provides some cooling effect, the amount of the cooling air is limited because a half of the coil end is closely covered by another coil end as shown in FIGS. 2 and 3 of the publication.
In JP-A-63-59744, the coil end has some spaces for reducing the resistance of a draft, and a cooling fan is provided to blow cooling air thereon in the radially outside direction to increase the cooling effect of the coil and other parts. However, this structure, in which a Lundell type rotor has an axially long field coil and thick pole-core-discs to provide sufficient magnetic field as shown in FIG. 1 of the publication, provides little benefits because the fan is positioned between the middle and the top of the coil end and does not cover the entire coil end. In other words, although the spaces for the cooling air in the limited portion of the coil ends which correspond to the fan allow the cooling air, to pass the cooling air does not cool all of the entire coil ends. Because drafting spaces are formed circumferentially at equal intervals to correspond to the winding pitch of the coil ends, the cooling air compressed by the fan blades is decompressed periodically at the drafting spaces, thereby making a siren sound or pitch noises.
In addition, the coil end units are shifted to provide spaces after the coil ends are aligned and flattened to have sufficient surfaces. As a result, the axial length of the coil end is increased.
JP-Y2-1-27406 shows spaces between coils of the same phase winding. However, it does not show spaces between coils of different phase windings JP-B2-4-24939 also does not show spaces between coils of different phase windings. For example, as shown in FIG. 4 of the publication, most portions of a coil end other than the section A--A is closely covered by another coil end of a different phase winding, thereby limiting the cooling effect.
Various attempts to dispose each element of a coil end have been made to improve the ventilation of the cooling air and the heat dissipation. Although each one of them has a structure which has spaces between coil elements of the same coil end and is aligned with another and flattened to provide a large cooling air passage, the passage is covered by another coil end thereby increasing the draft resistance. Moreover, only a limited portion near the fan is cooled and the fan noises increases considerably, causing problems in practical operation.